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991.
D Mangapathi Rao M Muralidhar T Somaiah V Hari Babu 《Bulletin of Materials Science》1991,14(2):199-206
Influence of sintering time and quenching in Bi2 −x
Pb
x
Ca2Sr2Cu3O
y
(x=0.0, 0.1, 0.2, 0.25, 0.3 and 0.4) samples have been studied by resistance and XRD measurements. In samples sintered at 850°C
for 4 days,T
c(0) increases with Pb concentration.T
c(0) increased from 81 K forx=0.0 to 109 K inx=0.30 sample and then decreased. Increasing the sintering time to 10 days decreased theT
c Quenching further decreased theT
c(0). From X-ray diffraction patterns, the intensity peaks of low and highT
c phases have been measured. The addition of Pb promotes highT
c-phase. Sintering time, slow cooling and rapid quenching studies show that there is an optimum sintering time and cooling
rate to produce a highT
c-phase. 相似文献
992.
本文主要研究用焦散线方法求解裂纹尖端应力强度因子,扼要介绍了焦散线法基本原理,并对单边裂纹拉仲板条的应力强度因子进行测量,与理论值相比较,符合得很好。 相似文献
993.
Air-holdup and heat-transfer coefficient values are measured in a 0.305 m diameter bubble column equipped with a seven-tube bundle for the air-water and air-water-glass bead system. The dependence of these two properties on air velocity (up to 0.28 m/s), temperature (297-343 K), glass bead powder average size (50-143.3 μm), solids concentration in the slurry (up to 20 weight percent) and bubble column diameter (0.108 and 0.305 m), is experimentally investigated. The effect of internals, as simulated by a single probe and a seven-tube bundle, in the two bubble columns is also examined. The models and correlations commonly employed to estimate these properties are assessed on the basis of generated data. 相似文献
994.
Srinivasan Palaniappan Chandrasekaran Saravanan Chellachamy Anbalagan Amarnath Vaidya Jayathirtha Rao 《Catalysis Letters》2004,97(1-2):77-81
Polyaniline salts are prepared by doping of polyaniline base with different Bronsted acids (H2SO4, HNO3 and H3PO4), organic acid — p-toluene sulfonic acid (PTSA) and Iodine (I2). Polyaniline complexes are also prepared using Lewis acids (BF3, AlCl3 and SnCl2). Polyaniline salts and polyaniline complexes are characterized by physical, electrical and spectral methods. Polyaniline salts and polyaniline complexes are used as catalyst for the first time in bisindole synthesis. Bisindole (3,3′-bis(indolyl)phenylmethane) is obtained in excellent yields with simple and more environmental benign procedure. The use of polyaniline catalysts are feasible because of their easy preparation, easy handling, stability, easy recovery, reusability, good activity and eco-friendly. 相似文献
995.
R. Johnson I. Ganesh B. P. Saha G. V. Narasimha Rao Y. R. Mahajan 《Journal of Materials Science》2003,38(13):2953-2961
The extruded cordierite honeycomb structure from a stoichiometric formulation of talc, kaolinite, and alumina was subjected to TGA-DSC, dilatometric and XRD investigations. The experimental observations were made to identify the phase transformation sequence in order to understand the solid state reactions involved in the cordierite formation. A maximum cordierite content of 90% was achieved for the samples sintered at 1693 K with a soaking time of 4 h, corresponding to a lowest coefficient of thermal expansion (CTE) of 0.74 × 10–6/K (along the direction of extrusion) was observed. Attempts were made to establish correlations with cordierite content, processing temperature and CTE of the samples. A few mechanisms are proposed to explain our observations. Attempts are also made to rationalize the low CTE observed along the direction of extrusion on the basis of orientation of anisotropic cordierite crystals as revealed by the transverse I-ratio calculated from the XRD patterns. Effect of CaO doping on CTE of cordierite has been studied in the present work. It was observed that though there is an increase in bulk thermal expansion of cordierite honeycombs on CaO doping due to the absence of micro-cracks as reveled by thermal cycling hysteresis, axial anisotropy was found to be reduced significantly. 相似文献
996.
A novel channel-allocation method that allows reduction of the four-wave mixing (FWM) effect while maintaining bandwidth efficiency is presented. It is composed of a fractional bandwidth-allocation algorithm, taking into consideration the use of parameters with distinct differences. This proposed technique allows the computation of an optimal channel-allocation set, where degradation caused by interchannel interference and FWM is minimal. Simulation is carried out to show significant performance improvement, such as an average bit-error rate improvement factor of 1.336 for an eight-channel wavelength-division multiplexing system, without the requirement of increased bandwidth, unlike existing channel-allocation methods. 相似文献
997.
A large proportion of antimicrobial peptides share a common structural feature that is critical to their antimicrobial activity, i.e. amphipathic alpha-helices. The amphipathy of a polypeptide chain can be quantitated through the value of the hydrophobic moment. Generally, antimicrobial peptides are characterized by high hydrophobic moment and low hydrophobicity values. Using these criteria we have identified two short segments that possess hydrophobic moment properties associated with known antimicrobial peptides. Using in vitro assays the segment derived from the protein perforin displays no antifungal or antibacterial activity and, while showing no alpha-helicity in buffer or liposomes, exhibits a modest degree of alpha-helical structure in the presence of the alpha-helical inducer, 2,2,2-trifluoroethanol. However, rational modifications result in a derivative which assumes an alpha-helical conformation in the presence of liposomes, exhibits potent antifungal activity against plant fungal pathogens, has significant antibacterial activity, effects leakage of a fluorescent dye from acidic liposomes and is devoid of hemolytic activity. Results are also presented for a segment derived from the human immunodeficiency virus envelope protein. We suggest that the identification of putative amphipathic structures in proteins may provide a useful starting strategy in the design and synthesis of antimicrobial peptides. 相似文献
998.
Ramgopal Rao V. Eisele I. Patrikar R.M. Sharma D.K. Vasi J. Grabolla T. 《Electron Device Letters, IEEE》1997,18(3):84-86
We have investigated gate oxide degradation as a function of high-field constant current stress for two types of oxides, viz. standard dry and LPCVD oxides. Charge injection was done from both electrodes, the gate and the substrate. Our results indicate that compared to dry oxides, LPCVD oxides show reduced charge trapping and interface state generation for inversion stress. The degradation in LPCVD oxides with constant current stress has been explained by the hydrogen model 相似文献
999.
1000.
A. Srinivasa Rao J. Lakshmana Rao R. Ramakrishna Reddy T. V. Ramakrishna Rao 《Optical Materials》1995,4(6):717-721
The Electron Paramagnetic Resonance (EPR) spectrum at 9.205 GHz and at 300 K has been examined for a series of Cr3+ ions doped alkali cadmium borosulphate [R2SO4-CdSO4-B2O3 (R=Li,Na,K or Cs)] glasses. The low field EPR spectral resonance lines are attributed to isolated Cr3+ ions where as the high field spectral resonance lines are attributed to exchange coupled pairs of Cr3+ ions. The absorption spectra of Cr3+ ions ions in these glasses show two broad bands characteristic of Cr3+ ions in octahedral symmetry. The bands are slightly shifted to higher wavelength side from Li glass to Cs glass. From the optical spectra the crystal field parameter Dq and the Racah interelectronic repulsion parameters B and C are evaluated. From the EPR and optical data, it is concluded that, the site symmetry around the Cr3+ ions is octahedral and the nature of bonding is predominantly covalent in nature. 相似文献